Orthogonal Click Chemistry Hydrogels for Culture and Differentiation of Pluripotent Stem Cells

Pluripotent stem cells (PSCs) are increasingly utilized to investigate early human developmental processes including gastrulation and organogenesis of endoderm-derived pancreatic lineages. Critical for tissue development, the PSC niche is a dynamic environment consisting of extracellular matrix (ECM) components that guide cell proliferation, migration, and differentiation. However, investigation of the interplay between the PSC niche and organogenesis has been limited to conventional two-dimensional (2D) cell culture or three-dimensional (3D) platforms requiring use of ill-defined materials (e.g., Matrigel). Furthermore, these systems lack tunability to probe specific qualities of the PSC niche including mechanical properties and biochemical compositions. In this dissertation, modular and dynamic hydrogels were designed to study PSC and niche interactions during differentiation and pancreatic organogenesis. Specifically, two bioorthogonal chemical reactions, thiol-norbornene photopolymerization and tetrazine-norbornene inverse electron demand Diels-Alder (iEDDA) reactions were employed to generate gelatin- and poly(ethylene glycol) (PEG)-based hydrogels with spatiotemporally tunable physicochemical properties. Following mechanical characterization of the hydrogels, the multicomponent gelatin-based hydrogels were assessed for supporting viability and pluripotency of human induced pluripotent stem cells (hiPSCs), as well as for permitting their trilineage differentiation. Next, fully synthetic PEG-based hydrogels with temporally tunable crosslinking density were established to probe the effect of matrix mechanics on definitive endoderm differentiation of the hiPSCs. Finally, hiPSC-to-pancreatic progenitor cell differentiation was explored in both naturally-derived gelatin-based hydrogels and synthetic PEG-based hydrogels, with cells differentiated on a 2D surface as a control. Overall, this work demonstrates that culture dimensionality, material compositions, and mechanics profoundly influence hiPSC differentiation and pancreatic morphogenesis.